Technology: Invisible ink that foils forgers

Invisible ink is the latest weapon to be used in the fight against the
forgery and counterfeiting of tickets and vouchers. When used to write on
genuine documents printed on special paper, the ink turns black. It remains
invisible on forgeries.

Colour photocopiers and laser printers are a godsend to the forger.
Peter Lee, a printing consultant who worked for the Bank of England for
30 years, says: ‘The new generation of copiers has put the skill of a trained
printer into the hands of the casual counterfeiter.’ It is now more effective
to add security features to paper at the mill than at the printing press.
Watermarks and metal threads, such as those used in British banknotes, cannot
be imitated accurately by even the most sophisticated copying equipment.

Nick Acland of Portals in Bathford, which makes paper for passports
and cheques, says: ‘It is very hard to counterfeit now unless you’re going
to make the paper, which is beyond the means of most counterfeiters.’

Europe’s largest paper maker, Wiggins Teape, manufactures the ink and
special paper to go with it. The ink, called IV or instant verification,
can be put into felt-tip pens or rubber-stamp pads. The paper contains a
chemical which reacts with the ink to make a black mark, but it looks like
ordinary paper, and can be watermarked and printed on. The company sees
the ink being used to check the authenticity of vouchers, record tokens,
postal orders and other documents that are used once and redeemed.

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Wiggins Teape and the Post Office patented the idea for the invisible
ink in 1974, but it has taken until now for reliable, safe chemicals to
be produced. Paul Thornton of Wiggins Teape says the chemicals are secret.
They are added at the start of papermaking, and have to be processed carefully
to make sure they are evenly distributed through the paper.

Joe Cassidy, who developed the chemicals, says: ‘The chemicals must
be very stable – the ink mustn’t go off.’ The company has tested the paper
and ink for nine months but is confident that both will still work in several
years’ time. ‘We have not found anything other than the ink that would react
with the chemical in the paper,’ said Thornton.